"Appending copy" command appends to clipboard (with separator) instead of replacing it

I find I need to copy multiple blocks of text and want them to be all one "paste" when I'm done so I don't have to keep switching between two documents. I'm imagining this command would allow an optional separator to be added to the task.

e.g., Let's say "Appending Copy" has its separator set to: ", "

I select "foo" and hit regular {copy} then
select "bar" and invoke {appending_copy}, and finally
select "baz" and {appending_copy}.

The result in the clipboard would be:
foo", "bar", "baz

I can now go to my 2nd document and type
to have a finished list
"foo", "bar", "baz"

(suitable for use as, say, elements in a javascript array).